Gas discharge lamps and incandescent lamps are well known in the art. Gas sources and incandescent lamps have relatively high energy consumption. Further, gas sources and incandescent lamps have relatively short lifetimes and are susceptible to breakage, typically leading to high maintenance costs. Further, the light intensity of gas discharge lamps tends to decrease over time with use. Additionally, gas discharge lamps typically produce ozone due to high voltage requirements and produce intense ultra-violet light that tends to cause the breakdown of many materials and may lead to gas leakage into the environment.
Solid state lighting, such as light emitting diode (LED) lighting has been developed to overcome some of the problems of gas discharge lamps and incandescent lamps. Many conventional LED devices, however, are limited by thermal energy-management issues.
It is known that LEDs exhibit negative temperature coefficient aspects, i.e. at fixed power input, as the device's operating heat rises, the device's light output decreases and it shortens the life of LED. Additionally, it is desirable to run LEDs using high current, because the higher the current, the higher the brightness of the emitted light. Further, high heat during use can shorten the useful life of an LED. Accordingly, there is motivation to remove heat as much as possible in order to operate an LED optimally with regard to power input and light output and LED life.
In addition, where a plurality of LED's are required for higher brightness, there are limits to how close they can be positioned next to one another due to the problem of heat dissipation. Accordingly, it is desirable to cool an LED device in order to maximize energy efficiency and lifespan as well as to broaden design options.
Conventional solutions to undesirable thermal buildup include fans, cooling fins, spacing assemblies, etc. to reduce lamp housing temperature. Another conventional solution involves mounting LED modules on large conductive heat sinks. A light emitting diode (LED) must be mounted on a relatively large metal heat sink to dissipate the heat when the diode is run using high current. In high use and in demanding situations, the thermal transfer from the LEDs through the thermally connected heat spreading plate to the housing is insufficient to maintain a desirable LED temperature. Unfortunately, thermal back-flow may occur as a housing is heated by the ambient atmosphere beyond an optimal point which allows thermal conduction back to the heat spreading plate. In such situations, rapid LED degradation often occurs and unit efficiency drops.
The above techniques for thermal removal have the common disadvantage of using direct passive conduction and convection heat transfer from the LED(s) to the heat sink or heat spreading plate and thereafter to the housing. The passive nature of these techniques limits the cooled temperature of the LED(s) to at or near an ambient atmospheric temperature. Since the units are often in close conjunction or are retained in decorative housings, passive heat transfer and thermal back-flow rapidly reduce cooling efficiency.
Solid state thermoelectric modules (TEM) also referred to as thermoelectric coolers (TEC) or heat pumps have been used in various applications. A TEM, in a thermocooling application, converts electrical energy into a temperature gradient, known as the “Peltier” effect. By applying a current through a TEM, a temperature gradient is created and heat is transferred from one side, the “cold” side of the TEM to the other side, the “hot” side.
The Peltier effect is well known by those skilled in the related arts and provides an active solid-state thermoelectric cooling function from a cool side to a hot side. The cool side is commonly placed against a surface or substrate which requires cooling. For example, the back surface of an LED assembly. The hot side is commonly placed against a surface or substrate which absorbs the transferred thermal energy and transfers it through conduction to a heat spreading plate. Through the utilization of these thermo-electric effects, thermal transfer from a cool side to a hot side can be controlled by controlling a current supplied to the thermo-electric effect.
Unfortunately, conventional constructions substantially negate the optimal use of an active cooling device by directly or indirectly connecting an LED or light array to a housing or heat spreading plate in a manner which allows thermal back flow to the lighting array through either thermal conduction or convection mechanisms.
There is a long-felt need for LED devices of long service life and high electric power-to-light efficiency.